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Lecture 3 Glycogen Synthesis - Biochemistry415/515 Glycogen...

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Biochemistry 415/515 Glycogen Metabolism Chapter 21 Berg • Tymoczko • Stryer Part II: Glycogen Synthesis
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Saving for Lean Times glycogen synthesis Dietary intake of glucose or carbohydrates frequently exceeds immediate need. Energy from excess glucose can be stored as fat or glycogen: Fat: More compact (cal/g), special storage site (white adipose), unlimited storage capacity Disadvantage: slow delivery; breakdown will not directly yield glucose unsuitable for brain Glycogen: Intracellular, limited storage capacity Advantage: readily available glucose reserve
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Glycogen metabolism glycogen glucose 1-P glucose 6-P glucose Glycogen phosphorylase Transferase Debranching enzyme Glucose 6-phosphatase (liver, kidney) hexokinase glucokinase phosphoglucomutase UDP-glucose pyrophosphorylase Glycogen synthase • Glycogenin Branching enzyme Synthesis from glucose (via uptake) or glucose 6-P (from gluconeogenesis) phosphoglucomutase Last lecture today
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Insulin increases the # of transporters at the cell surface Blood glucose levels fluctuate: Fasting: 3.9-5.6 mM After meal: 10 mM or more Transport of glucose into cells GLUT: A family of glucose transporters with distinct biochemical properties and tissue distribution
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After transport, phosphorylation: Glucokinase (liver) High K m Not subject to FBI by G-6-P
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Possible fates of glucose 6-phosphate Glycolysis Pentose phosphate pathway Glycogen synthesis (after conversion to glucose 1-P) Glucokinase (liver)
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Glycogen synthesis 1) Requires an activated form of glucose: UDP-glucose 2) UDP-glucose is added to the non-reducing ends of glycogen 3) Remodeling (branching) is needed for continued synthesis
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UDP-glucose is the glucose donor for glycogen synthesis UDP-glucose pyrophosphorylase “activated glucose” 2 P i Glucose 6-P reversible The hydrolysis of pyrophosphate drives the reaction phosphoglucomutase
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Glycogen synthase: adds glucosyl units Glycogen synthase adds glucosyl units to a chain >4 residues - glycogen chain - glycogen chain
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Glycogen synthesis begins with the protein glycogenin Glycogenin
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